1. Technical Field
This invention relates to an open web truss-type structural supports, and more specifically to an open web truss-type structural supports which is trimmable in length.
2. Background
A problem which frequently occurs on construction job sites is faced when joists or trusses are set in place. Oftentimes, the dimensions between the structural components which will bear the joists or trusses vary in their as-built dimension as opposed to the designed dimensions. Oftentimes, this variance may be measured simply as a matter of inches or fractions of inches. Nevertheless, this condition could lead to a situation where costly prefabricated materials would have to be discarded and refabricated.
A number of approaches have been taken to solve this problem. In Black, U.S. Pat. No. 3,078,970, a truss is disclosed which allows for longitudinal adjustment by means of a series of corresponding and overlapping holes located along the top and bottom chord members which may be selectively bolted together to adjust the overall length of the truss.
In Reetz, U.S. Pat. No. 4,745,724, a support member of adjustable length is disclosed. The means for adjusting the length of the member includes an adjustable length end web, pivotally attached at one end to the lower chord member and at the second end to a mounting bracket. The mounting bracket in turn is adjustably attachable to the upper chord member.
Black and Reetz address the problem of adjustability of structural members which are unique in the sense that they both deal with structural members which are prefabricated using metal structural components. Other solutions to the problem have been suggested by prefabricators of wooden structural components.
Open Joist Inc. of Brossard, Quebec, Canada, and Plattsburg, N.Y., produces an open web joist assembled of lumber and glue. The ends of the open web joists provide a solid web which spans between the upper and lower chord members, the edge portion of the solid web being butted up against the upper and lower chord members and glued to the upper and lower chord members, providing a length at either end of the joist which may be trimmed for length adjustment.
Similarly, Trim Joist of Columbus, Mo., fabricates an open web joist having a solid web end section glued in to a pair of grooves, one groove located on the lower face of the upper chord member and a second groove being located on the upper face of the lower chord member. The Trim Joist product design provides a series of inclined web members with the web member located at either end of the joist being positioned in the vertical or upright position, normal to the upper and lower chords.
Yet another product on the market is manufactured by a company known as Trus Joist Corporation, which provides a continuous, oriented strand board, or O.S.B., web where the top and bottom edges of the web are glued into a pair of grooves, one groove located on the bottom side of the upper chord member and a second groove located on the top side of the bottom chord member respectively. See Brightwell, U.S. Pat. No. 4,715,162, Wooden Joist With Web Members Having Cut Tapered Edges and Vent Slots.
Each of the above described lumber or wood product joists share one distinct disadvantage, that being that the prefabricated structural component must be fabricated in a relatively large facility in order to be capable of accommodating a prefabricated structural component, often times in excess of 30 feet in length. Because these structural components are prefabricated entirely or in part by gluing, the fabrication facility must maintain, at substantial cost, temperature and humidity controls in order to meet the strict quality control criteria required for these processes.
Therefore, one object of the present invention is to provide a design for a trimmable structural support member which allows the greatest portion of the structural support member to be prefabricated at a facility where the need for temperature and moisture control is eliminated.
Another object of the present invention is to provide a design which allows for the prefabrication of joist end subassemblies which would be readily insertable between the upper chord member and lower chord member of a conventional wood joist, thereby minimizing the cost of maintaining the facility in which the end sections are prefabricated while allowing for the conversion of a standard open web truss-type joist to an adjustable or trimmable joist.
Another disadvantage of previous wood product and lumber designs which employ a glued in solid web end section is found in the fact that oftentimes the glue joint, where the web is glued to a chord member, exhibits a propensity for "unzipping" or failing along the glue joint when the joist is placed under load.
Therefore, a third object of the present design is to minimize stress risers, or stress concentrations, which exist in trimmable open web truss-type joists at either end of the glue joint which secures the solid web section to the chord members.